chore(indexes): fix sidebar click error in demo (#3980)

* chore(indexes): fix sidebar click error in  demo

* chore: retain controlled usage

---------

Co-authored-by: anlyyao <[email protected]>

Author: novlan1

packages/components/indexes/_example/base/index.js

@@ -1,6 +1,6 @@
 Page({
   data: {
-    defaultCurrent: 'B',
+    current: 'B',
     indexList: [],
     list: [
       {
@@ -104,7 +104,9 @@ Page({
 
   onChange(e) {
     const { index } = e.detail;
-
+    this.setData({
+      current: index,
+    });
     console.log('change:', index);
   },
 

packages/components/indexes/_example/base/index.wxml

@@ -2,7 +2,7 @@
   <t-navbar title="TDesign" leftArrow />
 </view>
 <t-indexes
-  current="{{defaultCurrent}}"
+  current="{{current}}"
   index-list="{{indexList}}"
   sticky-offset="{{stickyOffset}}"
   bind:select="onSelect"